MPI (Message Passing Interface) has been defined as a standard for message passing communication in parallel environments and, even though MPI implementations, such as MPICH, work in heterogeneous non-dedicated environments (e.g., NOWs), they may need enhancements in order to promote security and performance. This work proposes the creation of a VPC (Virtual Private Cluster) to enhance the security of parallel applications executing in NOWs. In a VPC (Virtual Private Cluster), which is formed by a set of machines that belong to a NOW, an application executes in dedicated mode, i.e., with no interference from other applications or users. This is accomplished through the usage of local firewalls. The VPC includes an authentication mechanism to allow the elimination of the ".rhosts" file, which allows a user to login to different machines without providing a password, a major security flaw. The VPC will also provide a channel for computational steering, which will allow the user to communicate with the application executing in the VPC.